There is known a hydraulic excavator as a typical construction machine. The hydraulic excavator is configured with a multijoint type front work device that includes a boom, an arm, and a bucket (work devices) each rotatable in a perpendicular direction, and a machine body that includes an upper swing structure and a lower travel structure. Each section of the front work device is supported rotatably. Owing to this, when a linear finished surface (target excavation surface) is formed, for example, by a tip end of the bucket while an arm crowding operation toward the machine body is performed, then an operator needs to actuate the sections of the front work device in a combined fashion to make linear a locus of the tip end of the bucket and is required to have expertise.
To address the need, Patent Document 1, for example, discloses a technique for automatically changing a boom angle in such a manner that an orbit (excavation orbit) of the tip end of the bucket travels along the target excavation surface (also referred to as target surface) during excavation work as a support device for carrying out linear excavation. A function to automatically or semi-automatically control the actuators in response to operator's operation and to actuate the objects to be driven such as the boom, the arm, the bucket, and the upper swing structure is referred to as machine control.
Patent Document 1 describes that control means of the excavation support device changes a boom rotation angle in response to a change of an arm rotation angle so that the bucket tip end moves on the excavation orbit when the arm moves in an excavation direction, and changes the boom rotation angle in response to the change of the arm rotation angle so that the bucket tip end moves above the excavation orbit by a predetermined height when the arm moves in an opposite direction to the excavation direction.
Meanwhile, a necessary engine speed of an engine and necessary power (pump horsepower) of a hydraulic pump in the hydraulic excavator vary depending on a content of work; thus, it is preferable to change power of these power generators to appropriate values as needed. Operating the hydraulic excavator at an inappropriate engine speed and inappropriate pump power causes an increase of fuel consumption and a deterioration of operability. The engine speed can be manually adjusted by an engine control dial installed in an operation room. Generally, however, an operator often grips two operation levers by two hands, so that it is not easy for the operator to adjust the engine control dial in the state. Furthermore, it is difficult for the operator in the course of carrying out work to determine an optimum engine speed in response to the work by himself/herself.
Patent Document 2, for example, describes a control system for an engine and a hydraulic pump of a construction machine such as a hydraulic excavator, wherein a controller reads an engine load factor from an engine control section that controls an electronically-controlled fuel injection pump of the engine, calculates an effective engine load factor by performing a stabilization process, selects a work mode suitable for a content of work with the effective engine load factor used as a parameter, issues a command to change over the work mode when a sensor detects that an operation lever of a work actuator is not operated, and controls states of the engine and the hydraulic pump in such a manner that an engine speed and hydraulic pump input horsepower are equal to those corresponding to the work mode.